Many plants accumulate organic substances in quantities sufficient to be economically useful as chemical feedstocks or raw materials for various scientific, technological, and commercial applications. Economically useful organic substances serve as sources of industrial oils, resins, tannins, saponins, natural rubber, gums, waxes, dyes, pharmaceuticals, and many specialty products.
Plant chemicals are often classified as either primary or secondary metabolites. Primary plant metabolites are substances widely distributed in nature, occurring in one form or another in virtually all organisms. Secondary plant metabolites are compounds biosynthetically derived from primary metabolites and are more limited in distribution in the plant kingdom. Secondary metabolites are frequently accumulated by plants in smaller quantities than are primary metabolites.
Secondary plant metabolites present a broad range of medicinal properties. Many folk remedies are based on the isolation and purification of secondary metabolites from trees, shrubs, and flowers. Recently, some plant secondary metabolites have been found to exhibit cancer-inhibiting activity, or other activity related to inhibiting diseases. For example, camptothecin, colchicine, docetaxel, etopside, paclitaxel, podophyllotoxin, tetrahydrocannabinol, topotecan, vinblastine, vincristine, vindesine, betulinc acid, as well as others, have been found to have anticancer activity.
The use of secondary metabolites to treat diseases such as cancer or human immunovirus (HIV) has been impeded, in part, by the difficulty associated with synthesizing secondary plant metabolites, using conventionally industrial chemical techniques. Because secondary plant metabolites often have highly complex structures with many chiral centers that may impart biological activity, such complex compounds cannot by synthesized economically. As a result, there is a need for an inexpensive, efficient, bulk method for selectively extracting secondary metabolites from plants.